1. Field of the Invention
The present invention relates to a robot system for machining a workpiece by a tool unit attached to a distal end of a robot movable arm, and a method of machining with such robot. In particular, the invention relates to a robot system suitable for cutting an end of a pipe in a saddle shape and for forming a hole on a side face of the pipe, and a method of machining using the robot system.
2. Description of the Related Art
In recent years, there have been many cases in which pipes are used for parts of a suspension of an automobile. With increase of using pipes for parts of the automobile suspension, there has been an increase in machining operation for cutting an end face of a pipe W in a saddle shape and machining operation for forming a hole on a side face of a pipe part, as shown in FIG. 11. In the machining operation of cutting in a saddle shape and forming a hole on a side face of a pipe, a machining tool needs to operate accurately in a three-dimensional space and even when the machining operation is carried out by a robot, a path control function higher than that of an ordinary level is required.
When carrying out the machining operation by a robot on a workpiece which does not have platelike shape, such as a cylindrical workpiece, a workpiece having an elliptic section or a prism or a pyramid, in the conventional art, a cutting tool is attached at a distal end of a movable arm of a robot at a predetermined angle and the machining is carried out by totally operating a plurality of axes of the robot movable arms as shown in FIG. 13. In the case shown in FIG. 13, a cutting tool 2 of laser nozzle attached to the distal end of a movable arm 100 of the robot is brought to face the workpiece W of a pipe shape and a plurality of the movable arms of the robot are driven to turn the distal end of the movable arm 100 as shown by an arrow Q with respect to the workpiece W, thereby cutting the workpiece W or forming a hole on the workpiece W. As described, since the machining operation is carried out by totally operating the plurality of axes of the robot movable arm, accuracy of a machined face is lowered by vibration of the robot.
Further, in machining a workpiece of a pipe shape using a conventional robot, a cut face S1 of the pipe shaped workpiece W is made perpendicular to circumferential surface of the workpiece W as shown in FIG. 12a, and the machining to form a slant cut face S2 at an angle relative to the circumferential surface as shown in FIG. 12b can not be performed. When pipes are welded to join them as shown in FIG. 11, it is difficult to carry out a firm welding if the cut face S1 is perpendicular to a circumferential surface of a pipe as shown in FIG. 12a, and the machining of cutting a pipe in a saddle shape performed by the conventional robot is not suitable for the welding for forming a joint.